This invention relates generally to pressure transducers. More specifically it relates to a pressure transducer having improved calibration, particularly a pressure transducer which is to be mass-produced.
Pressure transducers are utilized in electrical or electronic circuits to provide pressure information input in the form of an electrical signal. While accuracy and reliability are always important considerations for a transducer, certain uses of pressure transducers include cost of the transducer as an important consideration. For example this is the case in the automobile industry.
Today's automobiles utilize electronic microprocessor based systems for information and control. The development of electronic technology has achieved significant cost-reductions and reliability improvements enabling acceptance by the automotive industry for mass production usage.
It is probably fair to state that automotive sensor development has not kept pace with that of electronics. This is not necessarily for lack of available sensors; rather the cost may have restricted the extent to which some sensors are used, or sensors themselves may lack the ability to meet the demanding performance specifications of the automobile industry. For a pressure transducer to meet acceptance for automotive use, it must be rugged, possess a reasonable degree of accuracy, have the proper package size, and be cost-effective.
One way to make a pressure transducer more costeffective in a mass production application is to automate its assembly and calibration to the fullest extent possible while still retaining its ability to meet performance specifications, and the present invention is directed to a new and unique pressure transducer which possesses these capabilities. It has a construction with an improved calibration adapted for massproduction by automated assembly and calibration procedures.
In a preferred embodiment the invention comprises an organization and arrangement of individual component parts which are cooperatively associated to enable the transducer's set point to be calibrated by automatic calibration equipment. For many uses of the transducer the set point calibration will be sufficient as the sole calibration step because the sizes and manufacturing tolerances on those component parts which affect accuracy will inherently yield an accurate calibration for the span as well. However, an extended aspect of the invention also contemplates the use of automatic calibration equipment to perform both set-point and span calibration steps in a manner whereby performance of one does not adversely influence the other. In other words for example, a span calibration step does not impair the set-point established by a preceding set-point calibration step.
The improved calibration of the pressure transducer of the invention is accomplished by means of an adjusting device, or devices, having interaction with the movement of the transducer in such a way that undesirable effects such as hysteresis, springback and the like are virtually eliminated. When both the set-point and the span are to be calibrated, such calibration is attained by independent steps which have no adverse interaction. In one preferred embodiment to be described, the calibration procedure comprises the set-point adjustment performed first, followed by the span adjustment; however, as noted, set-point calibration alone may be sufficient for many applications.
Moreover, the fabrication and assembly of individual component parts are accomplished by an efficient way so that there are a comparatively small number of component parts to be assembled together and the parts themselves can be fabricated by conventional techniques. For example, by making certain parts out of plastic, they can be fabricated by conventional plastic fabrication techniques, such as injection molding. Other parts can be fabricated by other conventional techniques such as stamping and forming.
The foregoing features, advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.